Methods for producing acetic acid

Abstract

A method produces acetic acid by continuously reacting methanol with carbon monoxide in the presence of a rhodium catalyst, an iodide salt, methyl iodide, methyl acetate, and water; and thereby producing acetic acid at a production rate of 11 mol / L·hr or more while keeping the acetaldehyde content of a reaction mixture to 500 ppm or less, in which the reaction is carried out at a carbon monoxide partial pressure in a gaseous phase of a reactor of 1.05 MPa or more and / or at a methyl acetate content of the reaction mixture of 2 percent by weight or more to thereby keep the production rate of acetaldehyde to 1 / 1500 or less that of acetic acid. This method can reduce production of by-products without reducing the reaction rate of acetic acid even at a low water content and a low hydrogen partial pressure in a reaction system.

Description

TECHNICAL FIELD[0001]The present invention relates to methods for producing acetic acid by reacting methanol with carbon monoxide in the presence of a rhodium catalyst.BACKGROUND ART[0002]A method for producing acetic acid by continuously reacting methanol with carbon monoxide using a rhodium catalyst and methyl iodide in the presence of water is one of the most excellent industrial production methods of acetic acid (refer to Patent Document 1). The original method, however, requires a great deal of energy to remove water in a purification process, since the resulting reaction mixture has a high water content. If the water content of the reaction mixture is reduced, the rhodium catalyst is inactivated and the productivity of acetic acid decreases.[0003]As a possible solution to reduce the water content of the reaction mixture without inactivating the rhodium catalyst, propose improved methods in which a catalyst stabilizer such as an iodide salt is added to the reaction system were ...

AI Technical Summary

Benefits of technology

[0033]According to the present invention, the formation of by-products can be reduced without reducing the reaction rate of acetic acid even at a low water content and a low hydrogen partial pressure of the reaction system. High-quality acetic acid can thereby be efficiently produced. Furthermore, acetic acid can be efficiently produced with a high productivity using simple processes and facilities while inhibiting the formation of acetaldehyde and consecutive reaction products thereof.

Problems solved by technology

The original method, however, requires a great deal of energy to remove water in a purification process, since the resulting reaction mixture has a high water content.

The methods, however, invite increase in by-produced carbonyl-containing reducing impurities to thereby decrease the quality of produced acetic acid.

Such an extremely low hydrogen partial pressure generally fails to ensure a sufficiently high catalytic activity in the production of acetic acid.

The production of highly pure carbon monoxide requires enhanced facilities for purification and invites increased cost.

Consequently, reducing substances such as crotonaldehyde and 2-ethylcrotonaldehyde as products consecutive reactions of acetaldehyde increase to thereby cause poor results in a potassium permanganate test of the product acetic acid.

This requires extra energy and an extra agent for removing water and thereby reduces the production efficiency.

This also increases the by-production of formic acid that is a reducing substance and causes poor results in a potassium permanganate test.

As a result, reaction products of acetaldehyde condensation increase to thereby impair the quality of acetic acid.

The reduction in hydrogen partial pressure, however, increases by-production of consecutive reaction products of acetaldehyde including acetaldehyde condensation reaction products to thereby impair the quality of acetic acid, as mentioned above.

Namely, it reduces the production efficiency of acetic acid and is industrially and economically undesirable.

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